This invention relates to dispersions of polyurethane and/or polyurea particles in an isocyanate-reactive material.
It is known to prepare dispersions of polyurethane particles in isocyanate-reactive materials. This is conveniently accomplished by the in situ reaction of a polyisocyanate with a low equivalent weight hydroxyl-containing "coreactant" (as defined herein) in the isocyanate-reactive material. The isocyanate-reactive material, although having groups which are reactive with the polyisocyanate, is generally a higher equivalent weight material such that the polyisocyanate predominantly reacts with the coreactant to form discrete particles dispersed in the isocyanate-reactive material, which forms a continuous phase. This process is described, for example, in U.S. Pat. No. 4,374,209, incorporated herein by reference. These polyurethane dispersions are commonly known in the art as PIPA polyols, and will be so referred to herein for convenience.
Dispersions of polyurea particles in an isocyanate-reactive material can be prepared in like manner by using certain nitrogen-containing compounds as coreactants, as described, for example, in U.S. Pat. Nos. 4,324,716; 4,310,449; 4,310,448; 4,305,857; and 4,305,858; incorporated by reference. The nitrogen-containing compounds include primary amines, secondary amines, hydrazines, dihydrazides, urea and ammonia. These polyurea dispersions are commonly known in the art as PHD polyols.
The foregoing dispersions can be used to prepare polyurethanes. The dispersion is reacted with a polyisocyanate, usually but not necessarily in the presence of a blowing agent, to form a cured polyurethane polymer. The polyurethanes prepared using these dispersions generally have good properties, particularly in the areas of load-bearing and in certain circumstances flammability, where significant improvements in burn properties, based on tests conducted under laboratory conditions, are often seen compared to polyurethanes made using conventional isocyanate-reactive materials.
A significant problem associated with these dispersions is that their use tends to produce foams which exhibit great amounts of shrinkage. This is particularly seen with the PIPA polyols. Although this invention is not limited to any theory, this phenomenon is believed to be due to poor cell-opening during the foaming process, causing the foam to contain large numbers of closed cells. Since the foam is hot when cured, as the foam cools the gases trapped in the closed cells contract. This in turn causes the pressure in the cells to drop, and the foam shrinks under the pressure of the surrounding atmosphere.
This problem can be partially overcome with the use of special cell-opening additives, or by mechanically crushing the foam after cure. However, these solutions require the use of additional components in the foam formulation, or additional process steps in the manufacturing process, both of which increase manufacturing costs. In addition, with PIPA polyols especially, these methods have found only limited use. Although useful, cell opening additives, most often do not eliminate the need for mechanical crushing. Similarly, crushing does not always fully eliminate the shrinkage, and often the foam must be crushed repeatedly or under severe conditions to adequately open the cells. This sometimes results in splits which render the foam unusable or require that it be repaired.
Another problem with these dispersions is that they tend to have a viscosity which is higher than desired. High viscosity makes these dispersions difficult to process, and limits the solids content of the dispersions.
Because of the other useful properties of PIPA polyols and PHD polyols, it would be desirable to provide a polyurethane and/or polyurea dispersion in an isocyanate-reactive material which provides for improved cell opening when made into polyurethane foam.